This invention recognizes the importance of early detection of potentially hazardous conditions causing increased ambient temperatures within electrical equipment. A high temperature event within a circuit breaker, an electrical panel, electric load center, or similar equipment can be symptomatic of many potentially dangerous conditions such as: loose, corroded, or faulty wire terminal connections; loose, burned, or corroded breaker-to-bus connections; an unbalanced circuit or distribution system; overloads; faults or defects in circuit breakers or other components; or worse, an electrical fire.
For such conditions to remain undetected can cause anything from minor intermittent power outages to total blackouts or catastrophic electrical fires. The consequences of these can be otherwise avoidable loss in productivity from equipment failure and unnecessarily expensive repairs that are caused by system components being burned or melted, which early detection might have avoided.
Because electric panels, load centers, motor controls, circuit breakers, and the like are not generally under constant visual surveillance, this invention recognizes a need for an alarm sensor with the capability of constantly monitoring the internal ambient temperatures within an electrical equipment enclosure and visually displaying an indication that an alarm event has occurred.
Other temperature indicators and alarms have been suggested for electrical equipment. These include the electric panel fire alarm of U.S. Pat. No. 5,461,367, which detects abnormally high ambient temperature within an electrical panel cabinet and actuates an alarm. This requires alarm components supplied with electrical power.
A self-adhesive high temperature indicator is available for use on circuit breakers. When the exterior of the circuit breaker reaches an alarm temperature, the indicator turns permanently from one color to another. While this type of indicator has some value, it suffers from a relatively short service life and must be discarded after experiencing a high temperature event.
Circuit breakers can visually indicate a tripped condition, as suggested in U.S. Pat. No. 3,443,258. While this type of indicator also has value, it depends upon the ability of the circuit breaker itself to trip when excessive current occurs. The June 1994 issue of ELECTRICAL CONTRACTOR reports on a study concluding that about half of circuit breakers installed for at least five years fail to trip when subjected to excessive current. A trip failure also fails to produce any visual indication.
Mechanical fire alarms such as suggested in U.S. Pat. No. 3,552,350 can produce a visual indication that an alarm motor spring has become unwound. While this can indicate the condition of the alarm spring, it does not necessarily indicate a high temperature event. Also, mechanical fire alarms have not been associated with electrical equipment and are too complicated and expensive to succeed as indicators in today's marketplace.